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Pyroelectric Detector!

Discussion in 'Electronic Basics' started by Natty, Sep 2, 2005.

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  1. Natty

    Natty Guest

    hello friends,

    I need ur help. I am using a PIR detector (IRA-E700STO SERIES MURATA)

    I dont get any changes in the output voltage when an infrared body

    is detected.. the output voltage ust produce a transition from either

    +ve to -ve or from -ve to +ve.. I dont get that..

    A PIR detector has an inbuilt FET. the pinout of the detector is the

    Drain, Source and the Ground.

    The detector is powered by supply connected to the drain.. and the

    out put from the source is used for further analysis. I am a bit

    confused.. I am not sure if something is wrong with the detector. I

    wud really appreciate ur suggestions. thanx in advance.

  2. Chris

    Chris Guest

    Hi, Natty. First, it's Drain, Source, and Gate. But your description
    of your test circuit is incomplete. Possibly you could look at the
    data sheet

    and then try a load resistor on the source, something like the
    applications circuit in the sheet with a 5VDC Vcc (view in fixed font
    or M$ Notepad):
    ` VCC
    ` +
    ` IRA-E700STO |
    ` |
    ` .----------. |
    ` | | |
    ` | D o---'
    ` | |
    ` | | Sig Out
    ` | |
    ` | S o-----------o-------o-------o
    ` | | | |
    ` | | | |
    ` | | .-. |
    ` | | | | 100K | 100pF
    ` | g o---. | | ---
    ` | | | '-' ---
    ` '----------' | | |
    ` | | |
    ` | | |
    ` === === ===
    created by Andy´s ASCII-Circuit v1.24.140803 Beta

    You could then amplify the output with an LM358 single supply op amp
    and then see if you can get an output.

    ` 1/2 LM358
    ` VCC
    ` +
    ` Sig Out |\|
    ` >--------|+\ Out
    ` | >--o-----o
    ` .---|-/ |
    ` | |/| .-.
    ` | | | |20K
    ` | === | |
    ` | GND '-'
    ` | |
    ` '---------o
    ` |
    ` .-.
    ` | |1K
    ` | |
    ` '-'
    ` |
    ` ===
    ` GND
    created by Andy´s ASCII-Circuit v1.24.140803 Beta

    It's likely you'll get a useable signal out of this. You also might
    want to use the other end of the LM358 as a slow comparator with a 10K
    pullup at the output to give you a CMOS-compatible logic signal.

    I'm also not sure what you mean by an "infrared body". Possibly you
    might want to try just sensing the flame coming off a cigarette lighter
    first, to see if your sensor works. The data sheet says your sensor is
    selective as to response frequency, with a 5um long pass filter. If
    you're using an narrow band infrared source (like an IR LED), it might
    be the wrong frequency to respond.

    Is any of this relevant? If not, could you describe what you're doing
    with the FET output of the sensor, and what you're sensing, in somewhat
    more detail?

  3. John Fields

    John Fields Guest

    The detector is doing just what it's supposed to do, which is to
    sense a _change_ in temperature and produce an output when it senses
    that change. What's happening is that when the sensor heats up it
    sends out a voltage of one polarity while it's heating up, and then
    when it starts cooling down it sends out a voltage of the opposite
    polarity while it's cooling down. During the times its temperature
    is steady, it does nothing.
  4. Natty

    Natty Guest

    Hello Chris and John,

    thank you so much for ur suggestions. I will try to sort it out the way
    u said. I think it is doing wat it has to do. Chris, I am trying to use
    it as a motion detector. i.e to detect the infrared radiation from our
    body. so it shud produce a pulse wen someone pass throu.. say across a
    particular door. I am using a dual element PIR. I will soon get back to
    you with my output. thanks again for ur reply.

  5. John Fields

    John Fields Guest

    Actually, it's Drain, Source and Ground.

    Note that the power supply is connected between the drain and ground
    and that the output signal appears across the source and ground.
    The gate of the FET is connected internally to the free end one of
    the series-opposed connected pyroelectric transducers, with the free
    end of the other transducer connected to ground. They're connected
    in series-opposition so that, for ambient temperature changes,
    they'll be inherently self temperature-compensating, while when a
    differential thermal signal hits one transducer the charge generated
    will be placed on the gate of the FET and converted to a voltage
    before it exits the package.
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